A conventional solar cell solar cell layer formation method mostly employs an expensive and time-consuming process such as sputtering, thermal evaporation, CVD, and PVD.
As an alternative method to the conventional method, techniques such as screen printing and ink-jet printing have been proposed. However, such conventional screen printing and ink-jet printing techniques has a disadvantage in that the solar cell layer formation is limited due to the contact problem of the screen printing technique and the discharge limitation of the ink-jet printing technique.
In other words, in FIGS. 1(a) and 1(b), there is shown a conventional electrode forming process employing the screen printing technique according to the prior art. In the conventional electrode forming process, a screen 3 formed at a screen frame 2 is disposed at a position corresponding to a substrate 1. Thereafter, a paste 6 is disposed on one side of the screen 3 having a through-hole 4 formed therein, and then is shifted from the left to the right on the drawing sheet in a state of being applied a vertical pressing force to thereby form a layer 6b on one side of the substrate 1 through the through-hole 4 of the screen 3.
Such a conventional screen printing technique has an advantage in that it has a remarkable excellence in terms of the manufacturing time and manufacturing cost as compared to another conventional photolithograph technique as enabling the electrode layer to be formed at room temperature and atmospheric pressure.
However, as shown in FIG. 2, the conventional screen printing technique entails a problem in that in a spreading area As of the left and right sides of the center having the maximum height h1, the layer 6b formed one side of the substrate 1 has a height lower than the maximum height h1, and thus the aspect ratio is considerably low, leading to a reduction in the light-receiving area of a solar cell and thus an increase in the shading loss, thereby deteriorating the efficiency of the solar cell.
As such, examples of a conventional typical CIGS thin film manufacturing process include a co-evaporation method, a sputtering method, an electro-deposition method, a molecular organic chemical vapor deposition (MOCVD) method. Such conventional various methods involve a problem in that a large area is difficult to implement, contamination is serious inside a vacuum device, and a thin film having a good quality is not easy to manufacture.
In addition, during the conventional CIGS thin film manufacturing process, in the case where the electro-deposition using a precursor, a spin coating method, a doctor blade method, and an ultrasonic spray method are employed, a solute such as copper, indium, or gallium is added to a solvent such as ethanol or propylene glycol to prepare the precursor to thereby produce a CIGS thin film using the above deposition methods. However, there occurs a problem in that since a carbon layer is present as a residue in the thus produced CIGS thin film, it significantly degrades the optical conversion efficiency.